DP, I have found my 998 to be off 2-3 tenths at trolling speed of .2 to .4 over that pretty accurate. It all has to do with the refresh rate of the antenna on mine which is the remote. I have heard that the internal like on the Helix models may be a little mor accurate. At running speed they are about as accurate as you can get. I am also one of those that fishes of my GPS map anymore more than depth finder. If your lakes are covered on it the new Lakemaster chart is the only way to go. Have Navionics and Lakemaster. Lakemaster much beter contours has color shading for depth and the nicest thing is lake level offset. You figure out wat depth lake is over or under normal pool then set your off set with the difference. Get you a foot or two of actual depth on any given day.